Ballards Ash

General discussion about trigpoints, the TrigpointingUK website etc

Re: Ballards Ash

Postby peregrinus » Wed Apr 27, 2016 10:58 pm

... and the other detail to Could do with formatting etc.

Still needs an explanation of how Passives are/were used though...
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Re: Ballards Ash

Postby ted » Thu Apr 28, 2016 8:19 am

Hi Bernie,

isn't it always the case that the second station replaced the first rather than existing concurrently?

I had assumed that the number was only to distinguish multiple stations of the same order in the same grid square.
But you are right that it also signifies that an earlier station has been replaced. That hadn't occured to me before,
but the OS agree with you :)

There are corner cases such as two FBMs and one Berntsen at Whitton Green H1TM5191 H2TM5191 H3TM5191

A bit of virtual digging finds this OS article: which states as follows:
The letter prefix in the Passive Station numbering system is largely a historical one indicating the origins of the station.

Stations prefixed with the letter 'B' are stations originally included in the SciNet (EUREF GB92) network of stations. Before the Active GPS Network these were of a higher order, however there is no longer any difference in quality between any of the designated Passive Layer stations.

Stations prefixed with the letter 'C' are stations which originally met the criteria for a National Network GPS (Passive Layer) station. Namely: have good aspect of the sky for GPS occupation; be accessible 24 hours a day to a two-wheel drive vehicle in all weather conditions; and permission for access, if required, easy to obtain. Most of these monuments were constructed specifically for GPS use, though where suitable, existing Fundamental Bench Mark or Triangulation monuments were adopted.

Stations prefixed with the letter 'H' or 'T' are Fundamental Bench mark or Triangulation monuments included in the Passive Network for transformation computation purposes, but do not generally meet the access requirements for a 'C' designated station.

The number immediately following these prefixes differentiates between stations when more than one exists within the same km square. Eg C2SZ3090, a station created in the km square SZ3090 to replace C1SZ3090 which has been destroyed.
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Re: Ballards Ash

Postby agentmancuso » Sat Apr 30, 2016 5:27 pm

Thanks Ted. I was familiar with that article on the previous version of the OS legacy site, but had lost track of it when they last jumbled things around!
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